If you want a vacuum for hard floors then you want something with a soft roller. Dyson makes a soft roller head that works with the V7, it's about $80-90, and there are knockoff ones on Amazon for $30 that will probably get you most of the way there.

If you want one vacuum to do it all, the Shark Duoclean vacuums work really well for hardwood and carpet, and they're fairly easy to maintain